Decorated moldings made of a plastic substrate with a silver plating layer formed thereon have a metal-like appearance and, therefore, can be used as interior parts of automobiles, such as meter clusters, center clusters and center consoles, or as exterior parts of automobiles, such as hubcaps, bumper moldings, wheel garnishes, grille radiators, back panels, door mirror covers and door handles, and in other fields of application than automobile parts, for example as air conditioner housings, and containers for cellular phones, notebook type personal computers, cosmetics, etc.
A method of producing such decorated moldings has been disclosed which comprises, for example, forming an undercoat layer on a substrate using a coating composition comprising an alkoxytitanium ester and at least one of an epoxy group containing-silane coupling agent and an epoxy resin and then forming a silver plating layer and a topcoat layer (cf. e.g. Japanese Kokai Publication Hei-10-309774, page 2).
The decorated moldings obtained by such a method of production have a basecoat layer, a silver plating layer and a topcoat layer formed in that order and, in silver plating layer formation, the so-called silver mirror reaction technique, which is a nonelectrolytic plating technique, is generally utilized. In producing such decorated moldings, such physical characteristics as silver deposition tendency, basecoat film smoothness, adhesion, film appearance are required. However, the conventional decorated moldings cannot always satisfy these requirements.
Other methods of producing decorated moldings, such as ones disclosed in Japanese Kokai Publication 2002-256454, page 2 and Japanese Kokai Publication 2002-256455, page 2, are also known. However, such methods of producing decorated moldings are not wholly satisfactory from the viewpoint of adhesion between the silver plating layer and basecoat layer, corrosion resistance of the laminate moldings obtained, silver plating layer deposition tendency, basecoat layer smoothness and/or appearance of the laminate moldings.
A coating composition to be applied to the silver surface which comprises a cold-curing silicone-acrylic resin has been disclosed as a technology of preventing discoloration of silver (cf. e.g. Japanese Kokai Publication Hei-06-57189, page 2). However, it is not entirely satisfactory from the appearance viewpoint, among others.
Accordingly, it is an object of the present invention to provide a base coating composition for decorated moldings containing silver plating layer and a top clear coating composition for decorated moldings containing silver plating layer, and decorated moldings obtainable by using these compositions; the compositions and moldings are to be excellent in silver deposition tendency, basecoat film smoothness, adhesion and film appearance.